1. Field of the Invention
The present invention relates to devices useful for pumping fluids and semisolids. More particularly, the present invention relates to devices such as double diaphragm pumps which are driven by a fluid.
2. Description of the Invention Background
Various devices have been developed which are useful for pumping fluids or semisolids and which are driven by some type of a fluid such as air. Many of such devices which use air, compress the air during a portion of the pumping cycle and then exhaust the compressed air to atmospheric pressure. If there is water vapor in the air, i.e., humidity, and it is not removed from the compressed air before it enters the pump, the cooling effect of polytropic, adiabatic expansion of the compressed air as it is exhausted can cause the water to freeze. As an example, if the relative humidity of the air is 40 percent and a volume of that air is compressed to one half of its original volume, the relative humidity of the air becomes 80 percent because the volume of the water does not significantly change. The temperature drop caused by adiabatic expansion of the compressed air from a pressure of 4.5 bar (approximately 65 psi) to atmospheric pressure, at a room temperature of 68 degrees Fahrenheit, is about 120 degrees Fahrenheit. Thus, when the air undergoes rapid adiabatic expansion, i.e., expansion without the addition of heat, the temperature of the air drops quickly and the moisture in the air freezes. When the moisture freezes it tends to build up in and block an exhaust passage of an air driven pump, and it eventually can completely shut off the exhaust passage, preventing operation of the pump. The temperature reduction can be so great that not only will the water vapor in the exhaust air freeze, but also the housing of the pump can become so cold that water vapor in the atmosphere will condense and freeze on the exterior of the pump.
Various air driven pumps have accordingly been designed which include some provision for reducing the freezing of water vapor entrained in the air which drives the pump, or for reducing blockage of an exhaust passage of the pump due to freezing of the water vapor. These pumps generally utilize either some type of air mixing or some type of moving element to attempt to reduce ice formation therein.